This invention concerns regenerative rectifier apparatus capable of ac-to-dc rectification and power regeneration from the dc load back to the ac supply.
A regeneration feature is often a requirement in a machine tool drive system in order to achieve rapid response to speed command changes. If a speed command to the motor of the machine tool is reduced and the motor is not under load, it is not necessary to wait for friction and windage losses to slow the motor down when regeneration is available to convert the energy in the rotational inertia of the motor to electrical energy.
In some prior art drive systems, the regenerated energy is returned to the dc link where it is dissipated in a resistor in series with a controlled switch. This method is undesirable because of the size and heat dissipation in the resistor and the reduction in system efficiency.
Other systems that return the regenerated energy to the ac supply require multiple thyristors connected between the ac system and the dc link. These thyristors require additional power rated commutation components to force commutate or turn-off the load current carrying thyristors. The commutation components are a multitude of reactors, capacitors, diodes and auxiliary power supplies. A system of this type is described in "The Forced Commutated Rectifier as a Regenerative Rectifier" by J. W. A. Wilson, IEEE Transactions on Industry Applications, Vol. IA-14, No. 4, July/August 1978, pps. 335-340. The present system does not require the use of dissipative resistors or complex force commutated thyristor circuits to achieve the return of regenerated energy to the ac supply.
An object of the present invention is to provide regenerative capability to an ac supply from an ac-to-dc-to-ac adjustable voltage, adjustable frequency, ac motor drive system.
Another object of the present invention is to provide regenerative capability to an ac supply from an ac-to-dc-to-dc adjustable voltage dc motor drive system.
A further object of the present invention is to provide in an ac-to-dc rectifier the capability of regeneration of power from a dc source at the output of the rectifier to the ac supply by reversing the direction of current flow from the output of the rectifier, rather than by reversing the rectifier output polarity.
A still further object of the present invention is to provide regenerative capability to a static ac-to-dc motor drive system by returning single phase power to the polyphase supply.